(2-imidazolin-2-ylamino) tetrahydroquinoxalines and methods for using same

ABSTRACT

A compound selected from the group consisting of those having the formula: ##STR1## and pharmaceutically acceptable acid addition salts thereof, wherein R 1  wherein R 1  and R 4  are independently selected from the group consisting of H and alkyl radicals containing 1 to 4 carbon atoms, R 2  and R 3  are independently selected from the group consisting of H, OXO, and alkyl radicals containing 1 to 4 carbon atoms, the 2-imidazolin-2-ylamino group may be in any of the 5-, 6-, 7- or 8- positions of the quinoxaline nucleus, and R 5 , R 6  and R 7  each is located in one of the remaining 5-, 6-, 7- or 8- positions of the qunioxaline nucleus and is selected from the group consisting of Cl, Br, H and alkyl radicals containing 1 to 3 carbon atoms. Such compounds, when administered to a mammal, provide desired therapeutic effects, such as alteration in the rate of fluid transport in the gastrointestinal tract, reduction in intraocular pressure, and increase in renal fluid flow.

BACKGROUND OF THE INVENTION

The present invention relates to novel substituted derivatives ofquinoxaline. More particularly, the invention relates to suchderivatives which are useful as therapeutic agents, for example, toeffect reduction in intraocular pressure, to increase renal fluid flowand to effect an alteration in the rate of fluid transport in thegastrointestinal tract.

Various quinoxaline derivatives have been suggested as therapeuticagents. For example, Danielewicz, et al U.S. Pat. No. 3,890,319discloses compounds as regulators of the cardiovascular system whichhave the following formula: ##STR2## where the 2-imidazolin-2-ylaminogroup may be in any of the 5-, 6-, 7- or 8- position of the quinoxalinenucleus; X, Y and Z may be in any of the remaining 5-, 6-, 7- or 8-positions and may be selected from hydrogen, halogen, lower alkyl, loweralkoxy or trifluoromethyl; and R is an optional substituent in eitherthe 2- or 3- position of the quinoxaline nucleus and may be hydrogen,lower alkyl or lower alkoxy.

SUMMARY OF THE INVENTION

The novel compounds of the present invention are those having theformula: ##STR3## and pharmaceutically acceptable acid addition saltsthereof, wherein R₁ and R₄ are independently selected from the groupconsisting of H and alkyl radicals containing 1 to 4 carbon atoms, R₂and R₃ are independently selected from the group consisting of H, O, andalkyl radicals containing 1 to 4 carbon atoms, the2-imidazolin-2-ylamino group may be in any of the 5-, 6-, 7- or 8-positions, preferably in the 6- position, of the quinoxaline nucleus,and R₅, R₆ and R₇ each is located in one of the remaining 5-, 6-, 7- or8- positions of the quinoxaline nucleus and is independently selectedfrom the group consisting of Cl, Br, H and alkyl radicals containing 1to 3 carbon atoms.

Particularly useful compounds are those in which R₁ and R₄ are H, R₂ andR₃ are independently selected from the group consisting of H and alkylradicals containing 1 to 4 carbon atoms, the 2-imidazolin-2-ylaminogroup is in the 6-position of the quinoxaline nucleus, R₅ is selectedfrom the group consisting of Cl, Br and alkyl radicals containing 1 to 3carbon atoms, more preferably Br, and is in the 5- position of thequinoxaline nucleus, and R₆ and R₇ are H.

Pharmaceutically acceptable acid addition salts of the compounds of theinvention are those formed from acids which form non-toxic additionsalts containing pharmaceutically acceptable anions, such as thehydrochloride, hydrobromide, hydroiodide, sulphate or bisulfate,phosphate or acid phosphate, acetate, maleate, fumarate, oxalate,lactate, tartrate, citrate, gluconate, saccharate and p-toluenesulphonate salts.

The present compounds provide one or more therapeutic effects, e.g., inmammals. Thus, these compounds are useful in a method for treating amammal in which one or more of these compounds are administered to amammal in an amount sufficient to provide the desired therapeutic effectin the mammal. Among the desired therapeutic effects provided by thepresent compounds include altering the rate of fluid transport in thegastrointestinal tract of a mammal; reducing or maintaining theintraocular pressure in at least one eye of a mammal; and increasing therenal fluid flow in at least one kidney of a mammal.

DETAILED DESCRIPTION OF THE INVENTION

The compounds of the present invention, i.e., 2-imidazolin-2-ylaminotetrahydroquinoxalines, are as described above. All stereoisomers,tautomers and mixtures thereof which comply with the constraints of oneor more formulae of the present compounds are included within the scopeof the present invention. For example, both tautomers ##STR4## arewithin the scope of the present invention.

The present compounds may be prepared in a manner analogous to theprocedures described in Danielewicz, et al U.S. Pat. No. 3,890,319 forthe production of the quinoxaline derivatives therein. This patent ishereby incorporated in its entirety by reference herein. Once a2-imidazolin-2-ylamino quinoxaline intermediate corresponding to thecompound described in Danielewicz, et al U.S. Pat. No. 3,890,319 isobtained, this 2-imidazolin-2-ylamino quinoxaline intermediate ishydrogenated to saturate any unsaturation at the 1-, 2-, 3-, and 4-positions of the quinoxaline nucleus.

Briefly, the 2-imidazolin-2-ylamino quinoxaline intermediates may beprepared by (1) reaction of the appropriate amino-quinoxaline withthiophosgene to form the corresponding isothiocyanate; and (2) reactingthis isothiocyanate with excess ethylene diamine to form thecorresponding beta-aminoethyl-thioureidoquinoxaline, which is thencyclized to the corresponding intermediate. Alternately, suchintermediates can be prepared by (1) reacting the correspondingaminoquinoxaline with benzoyl isothiocyanate to form the correspondingN-benzoyl thioureido compound, followed by hydrolysis to the thioureidocompound, or reaction of the aminoquinoxaline with ammonium thiocyanateto form the thioureido compound directly; (2) methylation to form theS-methyl deviation of the thioureido compound; and (3) reaction withethylene diamine to form the intermediate.

The 2-imidazolin-2-ylamino quinoxaline intermediate is then reacted tosaturate any unsaturation at the 1-, 2-, 3-, and 4- positions of thequinoxaline nucleus. For compounds in which R₁, R₂, R₃ and R₄ are all tobe H, the intermediate may be hydrogenated. This hydrogenationpreferably occurs with the intermediate dissolved in a liquid, e.g., alower alcohol such as methanol, ethanol or the like. A catalysteffective to promote the hydrogenation is preferably present. Examplesof such catalysts include the platinum group metals, in particularplatinum, platinum group metal compounds, such as platinum oxide, andmixtures thereof. Hydrogen, e.g., free molecular hydrogen, is present inan amount at least sufficient to provide the desired saturation,preferably in an amount in excess of that required to provide thedesired saturation, of the intermediate. The temperature and pressure atwhich the hydrogenation occurs are preferably selected to maintain theintermediate and final product substantially in the liquid phase.Temperatures in the range of about 10° C. to about 100° C. and pressuresin the range of about 0.5 atmospheres to about 5 atmospheres oftenprovide acceptable results. These conditions are maintained for a timesufficient to provide the desired hydrogenation reaction. This period oftime is often in the range of about 1 minute to about 2 hours. The final2-imidazolin-2-ylamino tetrahydroquinoxaline is separated from thehydrogenation reaction mixture and recovered, e.g., using conventionaltechniques.

For compounds in which R₁, R₂, R₃ and R₄ are all to be H and forcompounds in which R₁ and R₄ are to be H and R₂ and/or R₃ are to bealkyl, the intermediate may be reacted with a suitable hydride reducingagent. This reaction preferably occurs with the intermediate and thehydride reducing agent dissolved in a liquid. Any suitable hydridereducing agent may be employed. Examples of useful hydride reducingagents include Na BH₄, NaCNBH₄, LiAlH₄ and the like. The amount ofhydride reducing agent used should be sufficient to saturate all theunsaturation present at the 1-, 2-, 3- and 4- positions of theintermediate. Excess hydride reducing agent may be employed providedthat no deterioration of the final tetrahydroquinoxaline productresults. The liquid employed should be such as to act as an effectivesolvent for the intermediate and the hydride reducing agent, and mayalso function to facilitate, e.g., activate, the reaction between theintermediate and hydride reducing agent. Examples of useful liquidsinclude acetic acid, trifluoroacetic acid, tetrahydrofuran, diethylether and the like. The liquid employed is preferably selected so as toavoid excess hydride reducing agent reactivity. For example, whereLiAlH₄ is used as the hyride reducing agent, the liquid is preferablytetrahydrofuran, diethyl ether and the like. One or more co-solvents,e.g., lower alcohols, may also be used. The temperature and pressures atwhich the reaction occurs are preferably selected to maintain theintermediate and final product in the liquid phase. Temperatures in therange of about 0° C. to about 50° C. and pressure in the range of about0.5 atmospheres to about 2 atmospheres often provide acceptable results.Reaction time is chosen to allow the desired reaction to occur, and isoften in the range of about one minute to about one hour. The final2-imidazolin-2-ylamino tetraquinoxaline is separated from the reactivemixture and recovered, e.g., using conventional techniques, such asevaporation, deactivation of the excess hydride reducing agent,extraction and chromatographic separation.

For compounds in which R₁ and/or R₄ are to be alkyl, the intermediate(having no substituents corresponding to R₁ and R₄) may be reacted witha suitable hydride reducing agent in the presence of a selected aldehydeor aldehydes. The aldehyde or aldehydes used are selected based on thespecific R₁ and/or R₄ alkyl group or groups desired. For example, if R₁and/or R₄ is to be methyl, formaldehyde is used, if R₁ and/or R₄ is tobe ethyl, acetaldehyde is used, etc. The reaction conditions used aresimilar to those described in the immediately preceding paragraph exceptthat the reaction time is often in the range of about 1 hour to about 24hours. The amount of aldehyde used may vary depending on the finalcompound desired. A mixture of final compounds, i.e., a compound inwhich both R₁ and R₄ are alkyl mixed with compounds in which only one ofR₁ or R₄ is alkyl, may be produced by the reaction. One or moreindividual etrahydroquinoxalines of the present invention can beseparated and recovered from this mixture, e.g., using conventionaltechniques.

The present 2-imidazolin-2-ylamino tetrahydroquinoxalines are useful toprovide one or more desired therapeutic effects in a mammal. Among thedesired therapeutic effects are an alteration, preferably a decrease, inthe rate of fluid transport in the gastrointestinal tract of a mammal, areduction in or maintenance of the intraocular pressure in at least oneeye of a mammal; and an increase in the renal fluid flow in at least onekidney of a mammal. Thus, for example, the present compounds may beeffective as an anti-diarrhea agent, a medication for use in thetreatment or management of glaucoma, and/or a medication for use in thetreatment or management of kidney disease. One important feature of manyof the present compounds is that the desired therapeutic effect isachieved with reduced side effects, in particular with reduced effectson the blood pressure of the mammal to which the present compound isadministered.

Any suitable method of administering the present compound or compoundsto the mammal to be treated may be used. The particular method ofadministration chosen is preferably one which allows the presentcompound or compounds to have the desired therapeutic effect in aneffective manner, e.g., low medication concentration and low incidenceof side effects. In many applications, the present compound or compoundsare administered to a mammal in a manner substantially similar to thatused to administer alpha agonists, in particular alpha 2 agonists, toobtain the same or a similar therapeutic effect.

The present compound or compounds may be included in a medicationcomposition together with one or more other components to provide amedication composition which can be effectively administered. Such othercomponents, e.g., carriers, anti-oxidants, bulking agents and the like,may be chosen from those materials which are conventional and well knownin the art, e.g., as being included in medication compositions withalpha 2 agonists.

The present compounds are often administered to the eye of a mammal toreduce or maintain intraocular pressure in the form of a mixture with anophthalmically acceptable carrier. Any suitable, e.g., conventional,ophthalmically acceptable carrier may be employed. Such a carrier isophthalmically acceptable if it has substantially no long term orpermanent detrimental effect on the eye to which it is administered.Examples of ophthalmically acceptable carriers include water, inparticular distilled water, saline and the like aqueous media. Thepresent compounds are preferably administered to the eye as a liquidmixture with the carrier. The compounds are more preferably soluble inthe carrier so that the compounds are administered to the eye in theform of a solution.

When an ophthalmically acceptable carrier is employed, it is preferredthat the mixture contain one or more of the present compounds in anamount in the range of about 0.0001% to about 1%, more preferably about0.05% to about 0.5%, W/V.

Any method of administering drugs directly to a mammalian eye may beemployed to provide the present compound or compounds to the eye to betreated. By the term "administering directly" is meant to exclude thosegeneral systemic drug administration modes, e.g., injection directlyinto the patients blood vessels, oral administration and the like, whichresult in the compound or compounds being systemically available. Theprimary effect on the mammal resulting from the direct administering ofthe present compound or compounds to the mammal's eye is preferably areduction in intraocular pressure. More preferably, the present compoundor compounds are applied topically to the eye or are injected directlyinto the eye. Particularly useful results are obtained when the compoundor compounds are applied topically to the eye.

Topical ophthalmic preparations, for example ocular drops, gels orcreams, are preferred because of ease of application, ease of dosedelivery, and fewer systemic side effects. An exemplary topicalophthalmic formulation is shown below in Table I. The abbreviation q.s.means a quantity sufficient to effect the result or to make volume.

                  TABLE I                                                         ______________________________________                                        Ingredient         Amount (% W/V)                                             ______________________________________                                        (2-Imidazolin-2-ylamino)                                                                         about 0.0001 to about 1.0                                  tetrahydroquinoxaline                                                         Preservative       0-0.10                                                     Vehicle            0-40                                                       Tonicity Adjustor  1-10                                                       Buffer             0.01-10                                                    pH Adjustor        q.s. pH 4.5-7.5                                            antioxidant        as needed                                                  Purified Water     as needed to make 100%                                     ______________________________________                                    

Various preservatives may be used in the ophthalmic preparationdescribed in Table I above. Preferred preservatives include, but are notlimited to, benzalkonium chloride, chlorobutanol, thimerosal,phenylmercuric acetate, and phenylmercuric nitrate. Likewise, variouspreferred vehicles may be used in such ophthalmic preparation. Thesevehicles include, but are not limited to, polyvinyl alcohol, povidone,hydroxypropyl methyl cellulose, poloxamers, carboxymethyl cellulose,hydroxyethyl cellulose, and purified water.

Tonicity adjustors may be added as needed or convenient. They include,but are not limited to, salts, particularly sodium chloride, potassiumchloride, mannitol, and glycerin, or any other suitable ophthalmicallyacceptable tonicity adjustor.

Various buffers and means for adjusting pH may be used so long as theresulting preparation is ophthalmically acceptable. Accordingly, buffersinclude but are not limited to, acetate buffers, citrate buffers,phosphate buffers, and borate buffers. Acids or bases may be used toadjust the pH of these formulations as needed.

In a similar vein, ophthalmically acceptable antioxidants include, butare not limited to, sodium metabisulfite, sodium thiosulfate,acetycysteine, butylated hydroxyanisole, and butylated hydroxytoluene.

Other excipient components which may be included in the exemplaryophthalmic preparation described in Table I are chelating agents whichmay be added as needed. The preferred chelating agent is edetatedisodium, although other chelating agents may also be used in place ofor in conjunction with it.

The following non-limiting examples illustrate certain aspects of thepresent invention.

EXAMPLE 1 Preparation of5-Bromo-6-(2-imidazolin-2-ylamino)-1,2,3,4-tetrahydroquinoxaline1,2,4-Triaminobenzene dihydrochloride

To a suspension of 4-nitrophenylenediamine (Aldrich, 10 g, 65.3 mmol) inabsolute ethanol (240 ml) was added 600 mg of 10% by weight palladium oncharcoal catalyst. The container including the suspension was evacuatedand filled with hydrogen three times and the suspension was hydrogenatedat 18 psi until hydrogen uptake ceased. The reaction was slightlyexothermic and one refill of hydrogen was required. The resulting lightyellow solution, which darkens rapidly on contact with air, was filteredand concentrated to about 150 ml. Concentrated hydrochloric acid (12 ml)was added and the solid formed was filtered off. After drying in vacuoovernight, 12 g (a yield of 93%) of purple solid was obtained, m.p.224°-5° C. Using various analytical procedures, this solid wasdetermined to be 1,2,4-triaminobenzene dihydrochloride.

6-Aminoquinoxaline

Glyoxal sodium bisulfite adduct (Aldrich, 14.3 g, 50 mmol) was added insmall portions to a solution of 1,2,4-triaminobenzene dihydrochloride(9.8 g, 50 mmol) in 200 ml of 10% by weight sodium carbonate in water.The reaction mixture was heated to 100° C. for two hours and then cooledto 0° C. The crystals formed were filtered off and dried in vacuo togive a crude yield of 7.06 g (a yield of 97%) of brown crystals.Recrystallization from benzene gave 6.32 g (a yield of 87%) yellowcrystals, m.p. 157°-8° C. Using various analytical procedures, theseyellow crystals were determined to be 6-aminoquinoxaline.

6-Amino-5-bromoquinoxaline hydrobromide

6-Aminoquinoxaline (2.08 g, 14.4 mmol) was dissolved in 11.5 ml glacialacetic acid. The solution was cooled in water while a solution ofbromine (0.74 ml, 2.3 g, 14.4 mmol) in 1.5 ml glacial acetic acid wasadded slowly over 15 min. After stirring for an additional 30 min, theorange red solid formed was filtered off and washed thoroughly with dryether. The solid was dried in vacuo overnight to yield 4.44 g crudeproduct (a yield of 100%). The compound, 6-amino-5-bromoquinoxalinehydrobromide, had no definite melting point. A phase change (from finepowder to red crystals) was noticed at about 220° C. Decomposition wasobserved at about 245° C. It was used directly for the next step.

6-Amino-5-Bromoquinoxaline

The crude 6-amino-5-bromoquinoxaline from above was dissolved in waterand saturated sodium bisulfite solution was added until the resultingsolution tested negative with starch-iodide paper. The solution was thenbasified with 2N sodium hydroxide and extracted thoroughly with ethylacetate. The organic extract was dried over magnesium sulfate andconcentrated under reduced pressure to give the free base. The crudeproduct was recrystallized from boiling benzene to give yellow crystals,m.p. 155°-6° C. Using various analytical procedures, the yellow crystalswere determined to be 6-amino-5-bromoquinoxaline. The yield was 82%.

5-Bromo-6-isothiocyanatoquinoxaline

The crude hydrobromide product previously noted (4.27 g, 14.0 mmol) wasdissolved in 60 ml of water and thiophosgene (Aldrich, 1.28 ml, 16.8mmol) was added in small portions with vigorous stirring. After 2 hours,the red color of the solution was discharged. The solid formed wasfiltered off and washed thoroughly with water. After drying in vacuo at25° C., 3.38 g (a yield of 90%) of brick red crystals was obtained, m.p.157°-8° C. A portion of this material was further purified by columnchromatography to give white crystals, m.p. 157°-8° C. Using variousanalytical procedures, these crystals were determined to be5-bromo-6-isothiocyanatoquinoxaline.

5-Bromo-6(-N-(2-aminoethyl)thioureido)quinoxaline

A solution of the isothiocyanate (3.25 g, 12.2 mmol) in 145 ml benzenewas added to a solution of ethylenediamine (Aldrich, 5.43 g, 90.0 mmol)in 18 ml benzene at 25° C. over 2 hours. After stirring for a further 30min., the supernatant was poured off. The oil which remained was washedby swirling with dry ether three times and used directly for the nextstep.

A portion of this product was further purified by column chromatography(SiO₂, CHCl₃) for characterization. A white solid was recovered whichdecomposed at 175° C. with gas evolution (puffing). This white solid wasdetermined to be 5-bromo-6(-N-2-(aminoethyl)thioureido)quinoxaline.

5-Bromo-6-(2-imidazolin-2-ylamino)quinoxaline

The crude product from above was dissolved in 100 ml dry methanol andthe brown solution was refluxed for 19 hours until hydrogen sulfide gaswas no longer evolved. The mixture was cooled to room temperature andconcentrated to about 50 ml. The yellow solid was filtered off and driedin vacuo; weight 2.52 g (a yield of 70%), mp 242°-4° C.

As the crude product was insoluble in most common organic solvents,initial purification was achieved by an acid-base extraction procedure.23 g of the crude product was dissolved in 100 ml 0.5N hydrochloricacid. The turbid yellow solution was filtered to give a clear orangeyellow solution which was extracted twice with ethyl acetate (2×10 ml).The aqueous phase was cooled to 0° C. and basified with 6N sodiumhydroxide, keeping the temperature of the solution below 15° C. at alltimes. The yellow solid which precipitated was filtered off and washedthoroughly with water until the washings were neutral to pH paper. Thesolid was dried overnight in vacuo to give 1.97 g yellow solid, m.p.249°-50° C. The recovery was about 88%.

Further purification was achieved by recrystallization as describedbelow. The partially purified product from above was dissolved inN,N-dimethylformamide (about 17 ml/g) at 100° C. with vigorous stirring.The solution was filtered hot and set aside to cool overnight. Thebright yellow crystals were collected by filtration, m.p. 252°-3° C.Recovery was from 65-77%. Using various analytical procedures, thebright yellow solid was determined to be5-bromo-6-(2-imidazolin-2-ylamino) quinoxaline.

5-Bromo-6-(2-imidazolin-2-ylamino)-1,2,3,4-tetrahydroquinoxaline

A thick-walled Parr hydrogenation flask was charged with5-Bromo-6-(2-imidazolin-2-ylamino)quinoxaline (950 mg, 3.23 mmol),platinum oxide (95 mg) and 20 ml of methanol. The contents of the flaskwere contacted with hydrogen at 15 psi for 15 minutes. The resultingsolution was filtered through acid washed silicon dioxide, followed byevaporation of solvent. The resulting tan solid was chromatographed(SiO₂ ; 80/20 CHCl₃ /CH₃ OH saturated with NH₃ (g)) to yield 820 mg (ayield of 86%) of an off white soid, mp 218°-220° C. Using variousanalytical procedures, this off white solid was determined to be5-bromo-6-(2-imidazolin-2-ylamino)-1,2,3,4-tetrahydroquinoxaline.

EXAMPLE 2 Preparation of(±)2-Methyl-5-bromo-6-(2-imidazolin-2-ylamino)-1,2,3,4-tetrahydroquinoxaline2-Methyl-6-nitroquinoxaline

A solution of pyruvic aldehyde (Aldrich, 40% solution in H₂ O, 11.8 g,65.3 mmol) was added dropwise to a solution of4-nitro-1,2-phenylenediamine (Aldrich, 10 g, 65.3 mmol) in 150 ml of H₂O. The reaction mixture was heated to 80° C. for four hours. Thereaction was cooled to room temperature, diluted with H₂ O and extractedwith CHCl₃. The organic extracts were dried over MgSO₄ and evaporated toyield 10.7 g (a yield of 87%) of as a brick red solid. Using variousanalytical procedures, this solid was determined to be 2-methyl-6nitroquinoxaline.

2-Methyl-6-Aminoquinoxaline

A thick-walled Parr hydrogenation flask was charged with2-methyl-6-nitroquinoxaline (10.0 g, 52.9) and CH₃ OH (200 ml). Theflask was flushed with a stream of N₂ and 10% by weight palladium oncharcoal (500 mg) was added. The flask was pressurized with H₂ to 50 psiand maintained at this pressure for three hours. The reaction mixturewas filtered through acid washed silicon dioxide and concentrated invacuo to yield a tan solid. The crude material was chromatographed (SiO₂; 95/5 CHCl₃ /CH₃ OH saturated with NH₃ (g)) and recrystallized frombenzene to yield 7.4 g (a yield of 88%) of a tan solid. Using variousanalytical procedures, this tan solid was determined to be2-methyl-6-aminoquinoxaline.

2-Methyl-5-bromo-6-(2-imidazolin-2-ylamino) quinoxaline

By a series of reaction steps analogous to the reaction steps describedabove in Example 1, the title compound (mp. 260° C.) was preparedstarting with 2-methyl-6-aminoquinoxaline in place of6-aminoquinoxaline.

(+)2-methyl-5-Bromo-6-(2-imidazolin-2-ylamino-1,2,3,4-tetrahydroquinoxaline

A solution of 2-methyl-5-bromo-6-(2-imidazolin-2-ylamino) quinoxaline(40.5 mg, 0.132 mmol) in acetic acid was cooled to 10° C. and carefullytreated with NaBH₄ (5.0 mg, 0.132 mmol). The reaction mixture wasstirred for 15 minutes before the solvent was removed in vacuo. Theresidue was dissolved in H₂ O, treated with solid NaOH to pH 13 andextracted with CHCl₃. The combined organic extracts were dried overMgSO₄ and concentrated in vacuo to yield a yellow oil. The crudematerial was chromatographed (SiO₂, 80/20 CHCl₃ /CH₃ OH saturated withNH₃ (g)) to yield 21.8 mg (a yield of 53%) of a tan solid, mp 203°-205°C. Using various analytical procedures, this tan solid was determined tobe (±)2-methyl-5-bromo-(2-imidazolin-2-ylamino)-1,2,3,4-tetrahydroquinoxaline.

EXAMPLE 3 Preparation of (±) 3-Methyl-5-bromo-6-(2-imidazolin-2ylamino)-1,2,3,4 -tetrahydroquinoxaline 3-Methyl-6-aminoquinoxaline

Pyruvic aldehyde (Aldrich, 892 mg, 4.95 mmol, 40% solution H₂ O) wasadded dropwise to a stirred solution of 1, 2, 4-triaminobenzenehydrochloride (1.0 g, 4.95 mmol) dissolved in 10% aqueous Na₂ CO₃ (15ml). The mixture was heated at 100° C. for two hours before cooling toroom temperature. The mixture was extracted with CHCl₃. The combinedorganic extracts were dried over MgSO₄ and concentrated in vacuo toyield a brown solid. The crude product was chromatographed (SiO₂, 95/5CHCl₃ CH₃ OH saturated with NH₃ (g)) to yield 616 mg (a yield of 75%) ofa yellow crystalline solid. An analytical sample was prepared byrecrystallization from benzene, mp 170°-173° C. Using various analyticalprocedures, the solid was determined to be 3-methyl-6-aminoquinoxaline.

(±)3-Methyl-5-bromo-6-(2-imidazolin-2-ylamino)-1,2,3,4-tetrahydroquinoxaline

By a series of reaction steps analogous to the reaction steps describedabove in Example 2, the title compound (mp 250°-251° C.) was preparedstarting with 3-methyl-6-aminoquinoxaline in place of2-methyl-6-aminoquinoxaline.

EXAMPLE 4

Preparation of5-Bromo-6-(2-imidazoline-2-ylamino)-1,4-dimethyl-1,2,3,4-tetrahydroquinoxaline,5-Bromo-6-(2-imidazolin-2-ylamino)-1-methyl-1,2,3,4-tetrahydroquinoxalineand5-Bromo-6-(2-imidazolin-2-ylamino)-4-methyl-1,2,3,4-tetrahydroquinxoaline.

5-Bromo-6-(2-imidazolin-2-ylamino) quinoxaline (291 mg, 1 mmol) issuspended in CH₃ OH (2 ml) and treated with glacial acetic acid (1 ml).The reaction mixture is treated with NaCNBH₃ (252 mg, 4 mmol) andparaformaldehyde (450 mg, 5 mmol) and stirred at room temperature for4-8 hours. The reaction mixture is quenched with H₂ O (5 ml), basifiedwith solid NaOH (3 g) to pH>12 and extracted with CHCl₃. The CHCl₃extracts are dried over MgSO₄, concentrated invacuo and chromatographed(SiO₂, 80/20 CHCl₃ /CH₃ OH saturated with NH₃ (g)) to yield theindividual title compounds. Each of these title compounds is tested andis found to have one or more useful therapeutic effects which knownalpha 2 agonists exhibit.

EXAMPLE 5

Preparation of5-Bromo-6-(2-imidazolin-2-ylamino)-1,4-diethyl-1,2,3,4-tetrahydroquinoxaline,5-Bromo-6-(2-imidazolin-2-ylamino)-1-ethyl-1,2,3,4-tetrahydroquinoxalineand5-Bromo-6-(2-imidazolin-2-ylamino)-4-ethyl-1,2,3,4-tetrahydroquinoxaline

The individual title compounds are prepared using the method illustratedin Example 5 except that acetaldehyde (220 mg, 5 mmol) is substitutedfor paraformaldehyde and the reaction time is 6-12 hours instead of 4-8hours. Each of these title compounds is tested and is found to have oneor more useful therapeutic effects which known alpha 2 agonists exhibit.

EXAMPLES 6 TO 8

The three (3) tetrahydroquinoxaline derivatives produced in accordancewith Examples 1 to 3 were tested to determine what effect, if any, thesematerials have on intraocular pressure.

Each of these materials was dissolved in distilled water at aconcentration of 0.1% (W/V). Each of these solutions was administeredtopically and unilaterally to one eye of a drug-naive, unanesthetizedNew Zealand white rabbit in a single 50 micro liter drop. Thecontralateral eye received an equal volume of saline prior todetermining the intraocular pressure after the mixture was administered.Also, approximately 10 micro liters of 0.5% (W/V) proparacaine (topicalanesthetic) was applied to the corneas of each of the rabbits beforedetermining intraocular pressure. As a control test, six (6) otherdrug-naive, unanesthetized New Zealand white rabbits were treated andtested as described above except that no tetrahydroquinoxalinederivative was included in the solutions administered to the eyes.

The intraocular pressure was determined in both eyes of each rabbitbefore and after the solutions were administered. Such intraocularpressure determinations were made in the conventional manner usingconventional equipment.

Results of these IOP determinations were as follows:

    __________________________________________________________________________                               Difference In                                                                 Intraocular Pressure, percent                           Active                Initial Effect                                                                          Maximum Effect                                                                          Maximum Effect                 Example                                                                            Material              On Treated Eye                                                                          on Treated Eye                                                                          On Untreated                   __________________________________________________________________________                                                   Eye                                  ##STR5##             +10.7 ± 3.6                                                                          -16.0 ± 3.3                                                                          N.S.                           7                                                                                   ##STR6##             N.S.      -15.1 ± 3.3                                                                          -8.6 ± 2.4                  8                                                                                   ##STR7##             N.S.      -12.5 ± 2.2                                                                          N.S.                           Control                    N.S.      N.S.      N.S.                           __________________________________________________________________________     N.S. means that the effect was not statistically significant.            

N.S. means that the effect was not statistically significant.

These results indicate that all of5-bromo-6-(2-imidazolin-2-ylamino)-1,2,3,4 tetrahydroquinxaline (Example6), (±) 2-methyl-5-bromo-6-(2-imidazolin-2-ylamino)-1,2,3,4tetrahydroquinoxaline (Example 7), and (±)3-methyl-5-bromo-6-(2-imidazolin-2-ylamino)-1,2,3,4tetrahydroquinoxaline (Example 8) are effective to reduce intraocularpressure in the treated rabbit eye, i.e., the eye to which the activematerial was directly administered. The tetrahydroquinoxaline derivativein Example 6 had an initial effect in the treated eye of raising theintraocular pressure. The tetrahydroquinoxaline derivative in Example 7also resulted in reducing the intraocular pressure in the untreatedrabbit eye.

EXAMPLES 9 TO 11

The tetrahydroquinoxalines produced in Examples 1 to 3 were tested foractivity using the following in vitro methods.

Rabbit Vas Deferens: Alpha 2 Adrenergic Receptors

New Zealand white rabbits (2-3 kg) were killed by CO₂ inhalation and thevasa deferentia removed. The prostatic ends of the vasa deferentia (2-3cm lengths) were mounted between platinum ring electrodes in 9 ml organbaths and bathed in Krebs bicarbonate solution of the followingcomposition (millimolar): NaCl 118.0; KCl 4.7; CaCl₂ 2.5; MgSO₄ 1.2; KH₂PO₄ 1.2; glucose 11.0; NaHCO₃ 25.0; which solution was maintained at 35°C. and bubbled with 95% O₂ and 5% CO₂. The initial tension of the vasdeferens was 0.5 g. The tissues were left to equilibrate for 30 minutesbefore stimulation was started. Vasa were then field stimulated (0.1 Hz,2 ms pulse width at 90 mA) using a square wave stimulator (WPI A310Accupulser with A385 stimulus). The contractions of the tissue wererecorded isometrically using Grass FTO3 force-displacement transducersand displayed on a Grass Model 7D polygraph. Cumulativeconcentration-response curves were obtained for thetetrahydroquinoxaline being tested with a 4 minute contact time at eachconcentration. The reduction in response height was measured andexpressed as a percentage of the height of the response before theaddition of tetrahydroquinxoaline. Concentration response curves foreach of tetrahydroquinoxalines were plotted. The effective concentrationrequired for a 50% reduction in response height, expressed as EC₅₀, wereobtained from these curves and are set forth below.

Rabbit Aorta: Alpha 1 Adrenergic Receptors Rabbit Saphenous Vein: Alpha3 Adrenergic Receptors

Thoracic aorta and saphenous vein specimens were obtained from albinorabbits that were killed by CO₂ inhalation. The aorta and saphenous veinwere each cut into 3 mm rings. Tissues were placed in Krebs-Hensleitsolution of the following composition (millimolar): NaCl 119; KCl 4.7;MgSO₄ 1.5, KH₂ PO₄ 1.2; CaCl₂ 2.5; NaHCO₃ 25 and glucose 11.0. Thesolution also contained cocaine (0.1 millimolar) to block neuronaluptake and EDTA (30 micromolar) and ascorbic acid (5 micromolar) toprevent oxidation of the tetrahydroquinoxaline being tested. Tissueswere hung in 10 ml organ baths and tension was measured via Grass FT03force-displacement transducers. Resting tension was 1 g and 2 g for thesaphenous vein and aorta, respectively. The solution was gassed with 95%O₂ and 5% CO₂ and maintained at 37° C. Tissues were allowed toequilibrate for 2 hours before stimulation and the cumulative additionof the tetrahydroquinoxaline being treated was started. Tissuestimulation was performed as with the rabbit vas deferens, describedabove. The contractions of the tissue were recorded isometrically as forthe rabbit vas deferens assay. Cumulative concentration response curveswere obtained and the EC50 valve developed for eachtetrahydroquinoxaline tested in a manner similar to that for the rabbitvas deferens assay.

Results of these in vitro tests were as follows:

    __________________________________________________________________________    EC.sub.50,                                                                    nanomolar                                                                          Active                       Rabbit Vas                                                                           Rabbit                               Example                                                                            Material              Rabbit Aorta                                                                         Deferens                                                                             Saphenous Vein                       __________________________________________________________________________     9                                                                                  ##STR8##             1130 ± 207 (n = 8)                                                                1.75 (n = 1)                                                                         92 ± 19 (n = 6)                   10                                                                                  ##STR9##             6750 ± 116 (n = 3)                                                                35.3 ± 3.9 (n = 5)                                                                581 ± 29 (n = 2)                  11                                                                                  ##STR10##            1060 ± 271 (n = 3)                                                                21.3 ± 3.0 (n = 2)                                                                --                                   __________________________________________________________________________

n is equal to the number of times the particular test was run.

These results indicate that the present tetrahydroquinoxalines have someactivity with respect to all of the alpha 1, alpha 2 and alpha 3adrenergic receptors. However, these materials have a particularly highactivity with respect to the alpha 2 adrenergic receptors. Thus, thepresent tetrahydroquinoxalines are properly classified as alpha 2agonists.

EXAMPLE 12

The tetrahydroquinoxaline produced in Example 1 was tested for renal andblood pressure effects using the following method.

Young male (20-24 weeks old) Sprague-Dawley rats were used. Underketamine (60 mg/kg b.wt. i.m.) and pentobarbital (i.p. to effect)anesthesia, medical grade plastic tubes were implanted into theabdominal aorta and vena cava via the femoral vessels. In addition, aSilastic-covered stainless steel cannula were sewn in the urinarybladder. After the surgery, the rats were housed individually and wereallowed free access to food and water until the day of the experiment.

For about 7 to 10 days before surgery and during recovery, the rats wereaccustomed to a restraining cage by placement in the cage for 2 to 3hours every 2nd and 3rd day. The cage was designed for renal clearancestudies (a model G Restrainer sold by Braintree Scientific, Inc.,Braintree, Mass.). The animals' adjustment to the cage was judged by thestability of blood pressure and heart rate.

For an experiment, a rat was placed in the restraining cage, and thearterial line was connected to a Statham pressure transducer and aBeckman Dynograph R61 to monitor the mean arterial blood pressure,hereinafter referred to as MAP. The venous line was connected to aninfusion pump system for infusion of replacement fluid. Thetetrahydroquinoxaline was administered intraduodenally by cannula. Thebladder cannula was extended with a silastic tube to facilitatecollection of urine in preweighed tubes. The volume of urine wasmeasured gravimetrically. Body weight was recorded before and after theexperiment.

Throughout the experiments, 0.9% NaCl containing 10% polyfructosan(Inutest) and 1% sodium PAH was infused at a rate of 20 microliters/min.An equilibration period of 60 minutes was followed by two consecutive 30minute control clearance periods. Then, the tetrahydroquinoxaline wasadministered for 90 minutes. Urine collection was resumed 10 minutesafter the start of tetrahydroquinoxaline administration. By this timethe washout of the bladder cannula dead space (approximately 200microliters) was completed. Three additional clearance measurements weremade. Blood samples (150 microliters) were collected at the midpoint ofurine collections. Plasma was separated and saved for analyses, and thecells were resuspended in saline and returned to the animals. Water andsodium loss was carefully replaced i.v. by a variable speed infusionpump.

Results of these tests were as follows:

    ______________________________________                                        Dose of         Increase in                                                   Tetrahydro-     Urine Flow,                                                   quinoxaline of  microliters/                                                                             Increase in                                        Example 1,      min./100 g of                                                                            MAP,                                               mg/kg of body weight                                                                          body weight                                                                              mm Hg                                              ______________________________________                                        0.01             0         0                                                  0.03             4         0                                                  0.1             16         0                                                  0.3             24         2.5                                                1               32         8                                                  ______________________________________                                    

The test was run 3 times. The results at 0.1 mg/kg of body weight andhigher dosages represent statistically significant differences (i.e., ina conventional statistical analysis of the date, P is less than 0.05).

These results indicate that the present substituted quinoxalines producerelatively large renal effects. Further, these results show that suchrenal effects are produced without a correspondingly large effect on theblood pressure.

EXAMPLE 13

The tetrahydroquinoxaline produced in Example 1 was tested foranti-diarrheal effects and blood pressure effects using the followingmethod.

Cecectomies were performed in unfasted rats as follows. Under anesthesiawith methohexital (60 mg/kg. i.p.), a laparotyphlectomy was initiatedwith a 2 cm midventral incision. The cecum was lifted from the abdominalcavity and exteriorized onto a gauze drape. The cecal apex was freed bysevering the avascular area of the mesocecum. Next, a ligature of #1silk suture was positioned so as to occulude the cecum and itsvasculature without compromising ileo-colonic patency. After theligature was secured and ileo-colonic patency confirmed, the cecum wasresected, and the remaining exposed cecal mucosa was washed with salineand cauterized. The intestinal segment was then returned to theabdominal cavity, and the abdominal muscle facia closed with interrupted4/0 chromic-gut sutures. The dermal incision was closed with 9 mmstainless steel wound clips that were removed approximately 1 week postsurgery. An arterial line was also implanted into the abdominal aortaand vena cava via the femoral vessels, in a manner similar to thatdescribed in Example 10. Immediately following the surgical procedure,animals were returned to their cages and allowed free access to food andwater. Animals were permitted at least 48 hour recovery period beforebeing used in experiments.

The cecectomized rats were put into individual wire-bottomed cagesplaced over sheets of clean paper, and deprived of food and water forthe duration of the assay. The MAP was monitored, as described inExample 10, throughout the assay. Rats were given a 2 houracclimatization period prior to the start of the assay in order toeliminate sporadic episodes of anxiety-induced defecation. During thisperiod they were observed also for consistent occurrences of pelletedfeces; an animal producing other than a pelleted stool was disqualifiedfrom the study.

Diarrhea was induced with oral administration of 16,16-dimethylprostaglandin E₂ (dmPGE₂) in 3.5% EtOH. The tetrahydro-quinoxaline wasadministered by gavage after the onset of diarrheal episodes. The cagepapers were removed and examined at 30 minute intervals for dmPGE₂-induced diarrhea. Fecal output was recorded at each interval and fecalconsistency is assigned a numerical score in each experimental group asfollows: 1=normal pelleted stool; 2=soft-formed stools; 3=water stooland/or diarrhea. The fecal output index (FOI) is defined as thesummation of the number of defecation episodes and their rankedconsistency score within an observation period.

Results of these tests were as follows:

    ______________________________________                                        Dose of Tetrahydro-                                                                           Percent Reduction                                                                            Increase in                                    quinoxaline of Example 1,                                                                     in FOI versus  MAP,                                           mg/kg of Body Weight, p.o.                                                                    dmPGE.sub.2 Control                                                                          mm Hg                                          ______________________________________                                        0.01            17             0                                              0.03            60             0                                              0.10            57             0                                              0.30            76             0                                              1.00            98             0                                              3.00            98             10                                             10.00           100            25                                             ______________________________________                                    

These results indicate that the tetrahydroquinoxaline produced inExample 1 provided substantial anti-diarrheal effects. Further, theseresults show that such anti-diarrheal effects are produced with no or arelatively minimal effect in blood pressure.

While this invention has been described with respect to various specificexamples and embodiments, it is to be understood that the invention isnot limited thereto and that it can be variously practices within thescope of the following claims.

What is claimed is:
 1. A compound selected from the group consisting ofthose having the formula ##STR11## and pharmaceutically acceptable acidaddition salts thereof, wherein R₁ and R₄ are independently selectedfrom the group consisting of H and alkyl radicals having 1 to 4 carbonatoms, R₂ and R₃ are independently selected from the group consisting ofH, oxo, and alkyl radicals having 1 to 4 carbon atoms, the2-imidazolin-2-ylamino group may be in any of the 5-, 6-, 7- or 8-positions of the quinoxaline nucleus, and R₅, R₆ and R₇ each is locatedin one of the remaining 5-, 6-, 7- or 8- positions of the quinoxalinenucleus and is independently selected from the group consisting of Cl,Br, H and alkyl radicals having 1 to 3 carbon atoms.
 2. The compound ofclaim 1 wherein the 2-imidazolin-2-ylamino group is in the 6- positionof the quinoxaline nucleus, R₅ is in the 5- position of the quinoxalinenucleus and is selected from the group consisting of Cl, Br and alkylradicals having 1 to 3 atoms, and R₆ and R₇ are both H.
 3. The compoundof claim 2 wherein each of R₁ and R₄ is H.
 4. The compound of claim 2wherein R₂ and R₃ are independently selected from the group consistingof H and methyl radical.
 5. The compound of claim 3 wherein R₂ and R₃are independently selected from the group consisting of H and methylradical.
 6. The compound of claim 4 wherein R₂ and R₃ are different. 7.The compound of claim 5 wherein R₂ and R₃ are different.
 8. The compoundof claim 2 wherein R₅ is Br.
 9. The compound of claim 3 wherein R₅ isBr.
 10. The compound of claim 4 wherein R₅ is Br.
 11. The compound ofclaim 6 wherein R₅ is Br.
 12. The compound of claim 1 wherein theformula is: ##STR12##
 13. The compound of claim 1 wherein the formulais: ##STR13##
 14. A compound selected from the group consisting of##STR14## and pharmaceutically acceptable acid addition salts thereof.15. A medication composition comprising:an amount of a compoundeffective to provide a desired therapeutic effect in a mammal to whichsaid amount of said compound is administered, said desired therapeuticeffect being selected from the group consisting of (1) an alteration inthe rate of fluid transport in the gastrointestinal tract of saidmammal; (2) a reduction in the intraocular pressure in at least one eyeof said mammal; and (3) an increase in the renal fluid flow in at leastone kidney of said mammal, said compound being selected from the groupconsisting of those having the formula ##STR15## pharmaceuticallyacceptable acid addition salts thereof and mixtures thereof, wherein R₁and R₄ are independently selected from the group consisting of H andalkyl radicals having 1 to 4 carbon atoms, R₂ and R₃ are independentlyselected from the group consisting of H, oxo, and alkyl radicals having1 to 4 carbon atoms, the 2-imidazolin-2-ylamino group may be in any ofthe 5-, 6-, 7- or 8- positions of the quinoxaline nucleus, and R₅, R₆and R₇ each is located in one of the remaining 5-, 6-, 7 - or 8-positions of the quinoxaline nucleus and is selected from the groupconsisting of Cl, Br, H and alkyl radicals having 1 to 3 carbon atoms;and a carrier component combined with said compound in an amounteffective to facilitate the administration of said amount of saidcompound to said mammal.
 16. The medication composition of claim 15wherein the 2-imidazoline-2-ylamino group is in the 6- position of thequinoxaline nucleus, R₅ is in the 5- position of the quinoxaline nucleusand is selected from the group consisting of Cl, Br and alkyl radicalshaving 1 to 3 atoms, and R₆ and R₇ are both H.
 17. The medicationcomposition of claim 16 wherein each of R₁ and R₄ is H.
 18. Themedication composition of claim 16 wherein R₂ and R₃ are independentlyselected from the group consisting of H and methyl radical.
 19. Themedication composition of claim 18 wherein R₂ and R₃ are different. 20.The medication composition of claim 16 wherein R₅ is Br.
 21. Themedication composition of claim 15 wherein said formula is ##STR16## 22.The medication composition of claim 15 wherein said formula is ##STR17##23. The medication composition of claim 15 wherein said formula is##STR18##
 24. A method for reducing or maintaining the intraocularpressure in a mammalian eye comprising administering to a mammalian eyean effective amount to reduce or maintain the intraocular pressure inthe mammalian eye of a compound selected from the group consisting ofthose having the formula ##STR19## pharmaceutically acceptable acidaddition salts thereof and mixtures thereof, wherein R₁ and R₄ areindependently selected from the group consisting of H and alkyl radicalshaving 1 to 4 carbon atoms; R₂ and R₃ are independently selected fromthe group consisting of H, oxo, and alkyl radicals having 1 to 4 carbonatoms, the 2-imidazolin-2-ylamino group may be in any of the 5-, 6-, 7-or 8- positions of the quinoxaline nucleus; and R₅, R₆ and R₇ each islocated in one of the remaining 5-, 6-, 7- or 8- positions of thequinoxaline nucleus and is selected from the group consisting of Cl, Br,H and alkyl radicals having 1 to 3 carbon atoms.
 25. The method of claim24 wherein said compound is administered directly to the mammalian eye.26. The method of claim 24 wherein said compound is administereddirectly to the mammalian eye in an amount effective to reduce theintraocular pressure in the mammalian eye.
 27. The method of claim 24wherein the 2-imidazolin-2-ylamino group is in the 6- position of thequinoxaline nucleus, R₅ is in the 5- position of the quinoxaline nucleusand is selected from the group consisting of Cl, Br and alkyl radicalshaving 1 to 3 atoms, and R₆ and R₇ are both H.
 28. The method of claim27 wherein R₂ and R₃ are independently selected from the groupconsisting of H and methyl radical.
 29. The method of claim 27 whereinR₅ is Br.
 30. The method of claim 25 wherein said formula is: ##STR20##31. The method of claim 24 wherein said formula is: ##STR21##
 32. Themethod of claim 24 wherein said formula is: ##STR22##